1. Field of the Invention
The present invention relates to a method and apparatus for detecting the position of a component in an inkjet printer, and, more particularly, to a method and apparatus for detecting the position of a printhead in an inkjet printer.
2. Description of the Related Art
The alignment of inkjet printheads in an inkjet printer is usually achieved by controlling the tolerances during the manufacture of the printhead and printer. As printheads increase in size and customer quality expectations increase, aligning inkjet printheads solely by controlling tolerances becomes increasingly expensive.
A normal ink jet printer uses a scanning carriage to move the printhead back and forth across the print medium. After each printing pass, the medium is moved forward and stopped for the next print pass. To achieve full color output, three or four primary color printheads are used, with a full range of color achieved by mixing the primary colors in various proportions. When a single, integrated printhead contains all of the primary colors (such as cyan, magenta and yellow), their relative alignment on the final output is very well controlled, since their relative placement is controlled by existing photolithography processes and numerically controlled laser devices. However, as the need for higher throughput increases, the number of nozzles increases, and the possibility of integrating the various colors in a monolithic device becomes unfeasible. The drops of ink from each primary color are then generated from separate devices, and their relative placement is controlled by automatic placement equipment that has much looser tolerances. Even when the separate devices are placed on a single printhead unit, the achievement of tolerances approaching a pixel between colors is very difficult. If each color is placed on a separate printhead, and they are joined on a carriage assembly, the relative placement accuracy is even worse.
In existing printers, test pages are sometimes generated which can be used to adjust the relative placement of each color. This solution becomes less effective in a business inkjet environment, when less user intervention is desired, and consistent operation is expected when various supplies, such as a printhead, are replaced.
What is needed in the art is a method of automatically detecting the positions of printheads in both a scan direction and a paper feed direction, as well as the skew angle of each printhead relative to the paper feed direction. Printed information can then be automatically corrected for position and skew as shown in related application Ser. No. 09/827,805 filed on Apr. 6, 2001.
The present invention provides a sensor arrangement in an inkjet printer that produces direct feedback to correct for misalignment of printheads.
The invention comprises, in one form thereof, an inkjet printhead position detection system including a light emitting device emitting at least one beam of light having a first edge and a second edge nonparallel to the first edge. An inkjet printhead includes a light detecting device detecting the at least one beam of light as the inkjet printhead scans across the light. A time period between when the light detecting device crosses the first edge of the at least one light beam and when the light detecting device crosses the second edge of the at least one light beam is dependent upon a position of the inkjet printhead.
The invention comprises, in one form thereof, a method of detecting a position of an inkjet printhead, including emitting at least one light beam having a first edge and a second edge, the second edge being nonparallel to the first edge. A light detecting device is provided on the inkjet printhead. The inkjet printhead is scanned across the light. The first edge of the light beam is detected with the light detecting device during the scanning step. The second edge of the light beam is detected with the light detecting device during the scanning step. The position of the inkjet printhead is calculated dependent upon a time period between the detecting steps.
An advantage of the present invention is that the positions of printheads can be sensed in both a scan direction and a paper feed direction.
Another advantage is that the detection of printhead position can be performed automatically, i.e., without the need for human intervention.